In about 250 million years, all continents will converge to form Earth’s next supercontinent, Pangea Ultima. A natural consequence of the creation and decay of this supercontinent will be extremes in carbon dioxide levels due to changes in volcanic rifting and outgassing. New research shows that increased carbon dioxide, solar energy and continentality lead to increasing warming hostile to mammalian life.
Pangea Ultima temperature and habitability: (a) mammalian species diversity without the influence of humans; (b) habitable regions (green area) in the Pre-industrial simulation; (c-h) cold month mean temperature (CMMT; degrees Celsius); (c,f) warm month mean temperature (WMMT; degrees Celsius); (d,g) and habitable regions (green area); (e,h) under two end members of our sensitivity analysis: low-pCO2 conditions (280 ppm) Pangea Ultima planetary configuration (in 250 million years); (c-e) and high-pCO2 conditions (1,120 ppm) Pangea Ultima configuration (in 250 million years); (f-h) with global land surface temperature (GLST) (grid-weighted) indicated. Image credit: Farnsworth et al., doi: 10.1038/s41561-023-01259-3.
Tectonic processes, occurring in the Earth’s crust and resulting in supercontinent formation would also lead to more frequent volcanic eruptions which produce huge releases of carbon dioxide into the atmosphere, further warming the planet.
Mammals, including humans, have survived historically thanks to their ability to adjust to weather extremes, especially through adaptations such as fur and hibernating in the cold, as well as short spells of warm weather hibernation.
While mammals have evolved to lower their cold temperature survivable limit, their upper temperature tolerance has generally remained constant.
This makes exposure to prolonged excessive heat much harder to overcome and the climate simulations, if realised, would ultimately prove unsurvivable.
“The newly-emerged supercontinent Pangea Ultima would effectively create a triple whammy, comprising the continentality effect, hotter sun and more carbon dioxide in the atmosphere, of increasing heat for much of the planet,” said University of Bristol’s Professor Alexander Farnsworth.
“The result is a mostly hostile environment devoid of food and water sources for mammals.”
“Widespread temperatures of between 40 to 50 degrees Celsius, and even greater daily extremes, compounded by high levels of humidity would ultimately seal our fate.”
“Humans — along with many other species — would expire due to their inability to shed this heat through sweat, cooling their bodies.”
Although human-induced climate change and global warming is likely to be a growing cause of heat stress and mortality in some regions, research suggests the planet should largely remain habitable until this seismic landmass change in the deep future.
But when the supercontinent forms, findings indicate only somewhere between 8% and 16% of land would be habitable for mammals.
“It is vitally important not to lose sight of our current Climate Crisis, which is a result of human emissions of greenhouse gases,” said University of Bristol’s Dr. Eunice Lo.
“While we are predicting an uninhabitable planet in 250 million years, today we are already experiencing extreme heat that is detrimental to human health.”
“This is why it is crucial to reach net-zero emissions as soon as possible.”
In their research, the authors applied climate models, simulating temperature, wind, rain, and humidity trends for Pangea Ultima.
To estimate the future level of carbon dioxide the team used models of tectonic plate movement, ocean chemistry and biology to map out inputs and outputs of carbon dioxide.
“We think carbon dioxide could rise from around 400 parts per million (ppm) today to more than 600 ppm many millions of years in the future,” said University of Leeds Professor Benjamin Mills.
“Of course, this assumes that humans will stop burning fossil fuels, otherwise we will see those numbers much, much sooner.”
“The outlook in the distant future appears very bleak,” Professor Farnsworth said.
“Carbon dioxide levels could be double current levels.”
“With the Sun also anticipated to emit about 2.5% more radiation and the supercontinent being located primarily in the hot, humid tropics, much of the planet could be facing temperatures of between 40 to 70 degrees Celsius.”
“This work also highlights that a world within the so-called ‘habitable zone’ of a solar system may not be the most hospitable for humans depending on whether the continents are dispersed, as we have today, or in one large supercontinent.”
In addition, the research illustrates the importance of tectonics and continental layouts when conducting research into exoplanets.
Although the Earth will still be within the habitable zone in 250 million years’ time, for mammals the formation of a supercontinent with elevated carbon dioxide will make most of the world uninhabitable.
The findings, published in the journal Nature Geoscience, suggest the landmass layout for a distant world could be a key factor when determining how liveable it is for humans.
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A. Farnsworth et al. Climate extremes likely to drive land mammal extinction during next supercontinent assembly. Nat. Geosci, published online September 25, 2023; doi: 10.1038/s41561-023-01259-3
